Dear All
Good day
I am working in utility portion of Oil and Gas project. I should follow Canadian standards and codes or IEEE/ANSI in absence of that. A part of design work is cabling .Cables are 13.8 KV power, 480 V power and control and protection cables. I have following options, in the order of construction cost:
1- Direct burial
2- Trench
3- Cable Tray on the Pip Rack
4- Cable Tray on Cable Rack
I would like to have your expert opinion on advantage and disadvantages of each method.
Furthermore I would like to know how much is the safety clearances between electrical cables and gas pipes, water and steam pipes in each case, together with references to the relevant code or standard
Thank you
Homayoun

Some applicable standards :

API RP 540 Electrical Installations in Petroleum Processing Plants
NEMA VE 2 Metal Cable Tray Installation Guidelines
OSHA Occupational Safety and Health Administration
IEEE 576-2000 - IEEE Recommended Practice for Installation, Termination, and Testing of Insulated Power Cable as Used in Industrial and Commercial Applications
IEEE 1242-1999 “Guide for Specifying and Selecting Power, Control, and Special Purpose Cable for Petroleum and Chemical Plants”.
This Guide addresses wire and cable design, materials, testing and installation. Illustrations of typical constructions and details on applications. An extensive cross-referenced list of standards and technical papers, as they apply to the wire and cable in the industry.
IEEE 525-1992 - IEEE Guide for the Design and Installation of Cable Systems in Substations.

So many advantages and disadvantages ! - Need some time to check all the requirements for each cable routing.

Cable trays must be kept at a certain distance from steam piping, high and low pressure systems, and any other heat generating equipment. It is acceptable for perpendicular pipe crossings, cable trays be no closer than18 inches above the top of insulation on hot pipes up to 500°F. You can reduce the distance after check with Mechanical. When running parallel above pipes, the separation should be increased by 6 inches. If a separation can not be achieved , the crossings should be carefully evaluated for using heat shielding.

You need to do a detailed study applicable to cable sizing and verify if installation is acceptable based on standards listed above.

You can find also many other standards to do your work.

In the oil & gas facilities basically your cable system installation will probably run aboveground (A/G) via cable trays or underground (U/G) in direct burial or combination of both. You may refer with the National Electrical Code NFPA 70, ANSI/IEEE Standard 242 & 399, and API RP-505 for different derating factors of various installation that could safely deliver power at the receiving end and operates the loads. Always look at the safety of the project though followed with your value engineering. Direct burial (underground installation) is the most economical against other method you've mentioned, e.g. trench probably concrete, cable tray in piperack and cable rack. Other factors that will affect the size of the cables are the the configurations, i.e. trefoil or flat formation, touching each other or has cable clearances, these will affect cost of trench and cable tray dimensions.

Cable voltage drop has significant effect on the long runs of low voltage system the 480V level and the control and protection cables due to cable AC and DC component resistances, but has negligible effect on the 13.8kV cable system.

The minimum 300mm clearances (parallel, perpendicular, or crossing) of power and control cables against gas pipes, steam pipes, and water pipes in aboveground and underground installation is safe, You have to consider this parameter in cable sizing/analysis. However, the clearance increases if your installation is near to the communication and sensitive instrument signal cables to avoid interference. In this case, you may want to coordinate with other engineering discipline to achieve the objective of the project before discussing the value engineering.

1- Direct burial - with double the usual depth and explosion-proof on the top of cable the best, and reliable, stable, sustainable and economical

2- Trench - expensive to construct, and subject to flood, safety issues, and more..

3- Cable Tray on the Pip Rack - not economical, hard to maintain, susceptible to so many issues , and dangerous in case of pipeline sabotage

4- Cable Tray on Cable Rack , more or less same issues as number three

So, I guess it is your decision, but number one seems to be the best option

I suppose you are talking about outdoor routing options. The right selection of method depends highly on the climate conditions like temperature of air and soil, and type of soil (dry, wet, etc). A cheap structural choose might lead to oversized cables that will cost more.

I don't recommend direct burial, because although cheap, eliminates accessibility, future need for extra cables, replacement of cables with short circuit, etc.

Homayoun,
Selection of direct buried vs other mehods of routing is not a matter of choice but selected based on losses... economical reasons and safety. Usually, direct buried cable are used in locations not requiring trenches or there are no passage of heavy equipment . Usually , these places or installations are away from are the plant. The advantages for direct buried are fire protected and mechanical protection.

Trenching is often unwanted by the final client due to the risk of carbo-hydrates in the trench, causing it to become hazardous. Less important circuits an be direct buried such as lighting, etc.
Often the preference is for all process-related cabling to be run above ground, in cable ladders and trays.